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International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 19.5, p. 445
Section 19.5.3.1. Fibre diffraction patterns
aWhistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN 47907, USA, and bDepartment of Molecular Biology, Vanderbilt University, Nashville, TN 37235, USA |
As noted above, the diffraction pattern from a fibre is confined to layer lines because of the repeating nature of the polymer helix. The layer lines in reciprocal space are perpendicular to the fibre axis in real space. The layer line passing through the origin in reciprocal space is called the equator or zero layer line. The line in a diffraction pattern normal to the equator and passing through the origin is called the meridian. If the fibre axis is perpendicular to the incident X-ray beam, the recorded diffraction pattern is symmetric about both the equator and the meridian. If the fibre is not normal to the incident beam, the pattern is symmetric only about the meridian.
